MOTOR TERMINAL CONNECTIONS

Motor Classification • Most of the industrial machines in use

today are driven by electric motors

• Motors are classified according to the type of power used (AC or DC) and the motors principle of operation

FAMILY TREE OF MOTOR TYPES

Motor Standards • IEEE

– Institute of Electrical and Electronics Engineers

– Establishes the standard for motor testing and test methodologies

• NEMA – National Electrical Manufacturers

Association – Prepares the standards for motor

performance and classifications

DC Motor Connections • DC Motors

1. Used in industrial applications because the speed-torque relationship can easily be varied

2. Speed can be controlled smoothly

down to zero, immediately followed by acceleration in the opposite direction

DC Motor Connections • DC Motors

3. Can supply five times the rated torque without stalling

4. Dynamic braking or Regenerative

braking can be obtained on applications requiring quick stops thus limiting the need of mechanical brake

AC Motor Connections • The AC induction motor is the

dominant motor technology in use today

• Representing more than 90 percent of installed motor capacity.

AC Motor Connections • Available in single-phase and three-

phase configurations, in sizes ranging from fractions of a horsepower to tens of thousands of horsepower.

• They may run at fixed speeds— most commonly 900, 1200, 1800, or 3600 rpm—or be equipped with an adjustable-speed drive.

MOTOR NAMEPLATE AND TERMINOLOGY

Motor Nameplate • Contains important information about

the connection and use of the motor.

• An important part of making motors interchangeable is ensuring that nameplate information is common among manufacturers.

Required Nameplate Information

• Motor Manufacture • Voltage Rating • Current Rating • Line Frequency • Phase Rating • Motor Speed • Ambient Temperature

Required Nameplate Information

• Temperature Rise • Insulation Class • Duty Cycle • Horse Power Rating • Code Letter • Design Letter • Service Factor

Required Nameplate Information

• Motor Enclosure • Frame Size • Efficiency • Power Factor • Thermal Protection • Connection Diagram

Guide to Motor Terminology • Across-the-line

– A method of motor starting. Connects the motor directly to the supply line on starting or running. (Also called full voltage.)

• Automatic starter

– A self-acting starter. Completely controlled by the master or pilot switch or some other sensing device.

• Auxiliary contact

– The contact of a switching device in addition to the main circuit contacts. Operated by the contactor or starter.

Guide to Motor Terminology • Contactor

– A type of relay used for power switching.

• Jog – Momentary operation. Small movement of a

driven machine.

• Locked-rotor current – Measured current with the rotor locked and

with rated voltage and frequency applied to the motor.

Guide to Motor Terminology • Low-voltage protection (LVP)

– Magnetic control only; not automatic restarting. A three-wire control. A power failure disconnects service; when power is restored, manual restarting is required.

Guide to Motor Terminology • Low-voltage release (LVR)

– Magnetic control only; automatic restarting. A two-wire control. A power failure disconnects service; when power is restored, the controller automatically restarts.

• Magnetic contactor

– A contactor that is operated electromechanically.

• Multispeed starter – An electric controller with two or more speeds

(reversing or non-reversing) and full or reduced voltage starting.

Guide to Motor Terminology • Overload relay

– Running over-current protection. Operates on excessive current. It does not necessarily provide protection against a short circuit. It causes and maintains interruption of the motor from a power supply.

• Plugging

– Braking by reverse rotation. The motor develops retarding force.

• Push button

– A master switch that is a manually operable plunger or button for actuating a device, assembled into pushbutton stations.

Guide to Motor Terminology • Reduced voltage starter

– Applies a reduced supply voltage to the motor during starting.

• Relay

– Used in control circuits and operated by a change in one electrical circuit to control a

Guide to Motor Terminology • Remote control

– Controls the function initiation or change of electrical device from some remote point.

• Selector switch – A manually operated switch that has the same

construction as push buttons, except that rotating a handle actuates the contacts. The rotating cam may be arranged with incremental indices so that multiple positions can be used to select exclusive operations.

• Slip

– The difference between the actual speed (motor rpm) and synchronous speed (rotation of the magnetic field).

Guide to Motor Terminology • Starter

– An electric controller used to start, stop, and protect a connected motor.

• Timer

– A pilot device, also considered a timing relay, that provides an adjustable time period to perform its function. It can be motor driven, solenoid actuated, or electronically operated.

• Torque

– The twisting or turning force that causes an object to rotate. There are two types of torque that are considered for looking at motors: starting torque and running torque.

MANUAL AND MAGNETIC MOTOR STARTER

Manual Starter

Manual Starter • Very basic way to supply power to a

motor.

• Manual control circuit is a circuit that requires the operator to control the motor directly at the location of the starter.

• Dotted line across the contacts designates a manual starter.

Manual Starter • Manual starters are operated by the

manual start/stop mechanism located on the front of the starter enclosure.

• The start/stop mechanism moves all three contacts at once to close (start) or open (stop) the circuit to the motor.

• The National Electrical Code requires that a starter not only turn a motor on and off but also protect it from overloads.

Manual Starter • The three thermal overload protective

devices are installed to mechanically trip open the starter contacts when an overload condition is sensed.

• Manual three-phase starters are used in low horsepower applications such as drill presses and table saws where remote pushbutton control is not required.

Magnetic Starter

Magnetic Starter • Magnetic motor starters allow a motor to

be controlled from any location.

• When the starter coil is energized, the three main contacts as well as the holding contact close.

• Should an overload condition occur, the normally closed OL relay contact would open.

Magnetic Starter • In addition to the power circuit, the

manufacturer provides some control circuit wiring.

• In this case the prewired control circuit wiring consists of two connections to the starter coil.

• One side of the starter coil is factory wired to the overload relay contact and the other side to the holding contact.

Types of Magnetic Control Circuits

Types of Magnetic Control Circuits

• Two-wire control circuit – Provides low-voltage release but not low-

voltage protection

– The starter deenergizes during power interruption but also reenergizes if the control devices remains closed during power restoration

Types of Magnetic Control Circuits

Types of Magnetic Control Circuits

• Three-wire control circuit – Provides low-voltage protection

– The starter will drop out during power

interruption but will not pick up during power restoration